THE KAINOZOIC ERA.

CHAPTER XI.

THE EOCENE AND MEIOCENE LIFE-PERIODS.

Origin of the TERTIARY formations-Eocene climate and sub-tropical vegetation Fossil forests - Nummulites. Extinction of some molluscs. Fishes Reptiles Serpents, cetacea

Deinocerata

Palæotheria Equine forms-Marsupials-Bats-Carnivora (?)– Birds-Tropical character of Meiocene flora in northern latitudesCetacea, tortoises, and insects-Carnivora, rodents-The "sabretoothed" lion-Giraffes, camels, sloths, bats, apes-Large herbivorous animals, Brontotherium, Titanotherium, Deinotherium, Sivatherium, Mastodon, rhinoceros, and hippopotamus.

THE formations of the TERTIARY era owe their origin in a very great measure, no doubt, to disintegration of earlier rocks, and particularly those of Cretaceous age. So greatly has denudation affected these latter, that in some very large areas there is no conformability whatever. between their strata and the Eocene beds. Chalk flints, usually much water-worn, constitute immense deposits of gravel, and a few characteristic Cretaceous fossils are distributed amongst the new formations. Thus a

sharp line has been drawn, behind which lie many once predominant forms-such as the enaliosaurs, plesiosaurs, pterodactyles, belemnites, ammonites, etc.—and the survivals are few and unimportant. On the Eocene side of the line, however, numbers of new genera have come into existence, the approximation towards existing types becomes progressively closer, and the proportion of species related to extinct types decreases, while the proportion of those allied with living forms increases very rapidly throughout the TERTIARY era. In America, the break between the SECONDARY and TERTIARY eras does not appear to be considerable; indeed, in certain localities, the rocks are entirely conformable, and we may therefore hope to find there some connecting links between the Cretaceous and Eocene life-forms which have been lost in the European area-a hope much strengthened by the recent discoveries of Marsh and Cope.

In Early and Middle TERTIARY times, at all events, the temperature of the Northern hemisphere must have been much higher than at present. European rocks of this era have yielded representatives of the American sequoia, taxodium, robinia, etc.; of the Asiatic planes, cinnamons, etc.; and of the Australian eucalyptus, Banksia, etc. In Spitzbergen Meiocene beds we have the taxodium, pine, poplar, willow, elm, etc., and a waterlily; besides considerable deposits of coal in Grinnell Land, beyond the eighty-first degree of north latitude. In the estuarine waters which deposited the London clay, lived species of large nautilus, together with corals and

other witnesses to a temperature probably averaging 15° Fahr. higher than in our time.

The co-existence in Europe of exotic flora with those characteristic of temperate regions, suggests a continuity of land surfaces over which the plants migrated, for their abundance and excellent preservation indicate that they grew in situ, and were not brought by ocean currents from distant lands and accidentally cast ashore. The seeds might doubtless have been so transported; but they could not have established themselves had they not found a genial climate, and it is impossible to entertain the idea that leaves could have been carried any distance and still have retained all their delicacy of structure. Among many instances of this may be mentioned the collection of thousands of leaves of spice plants, palms, taxodium, and other exotics, from the Eocene sands and clays of South Hampshire, by Mr. J. Starkie Gardner, which frequently exhibit the minutest details of the original venation and woody fibres.

Among the interesting objects brought to light by the United States Geological Survey, none surpass the fossil TERTIARY forests of the Yellowstone region. Trunks of trees are found here on the banks of the Yellowstone river, standing upright in rows one above the other, from the top to the bottom of the cliffs, like the columns of a temple. These splendid silicified trunks, from twenty to thirty feet in height, rivalled their mighty descendants, the Wellingtonias, in bulk. Forest stands piled upon forest through strata 4000 feet thick, which must have

been the result of many alternations of sea and land occupying a vast period.

The general aspect of the TERTIARY flora leads to the conclusion that the existing vegetation of the globe has descended directly from botanical types which, for the most part, appeared first during this era in any considerable force, although some were distinctly foreshadowed in the Later SECONDARY.

A striking feature of the Eocene period is the inconceivable abundance of such low forms of life as the foraminifers. Certain members of this group, the nummulites-coin-shaped shells, about an inch in diameter— constitute a large portion of the mountain systems of the

FIG. 32.-Nummulites; from the stones of which the Great Pyramid is built (actual size). No. 1. a section of the shell, showing the internal chambers; Nos. 2 and 3. with part of the surface layer removed.

Old World—the Alps, Pyrenees, Carpathians, the Atlas and its spurs, and the great chain which passes through Northern Persia, Hindustan, and Tibet-an area alto

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gether of vast extent. And this stupendous formation, rising at some points more than 16,000 feet above the level of the sea, is the work of a marine shell-fish— calcareous matter deposited by a lowly foraminifer at the bottom of an Eocene ocean, and subsequently raised to the position it has maintained until this day.

Not to dwell upon the numerous mollusca of the period, it may be sufficient to observe that they are still approaching more closely to existing forms; while the ammonites, belemnites, and hippurites are extinct, and never again appear in any strata of undoubted TERTIARY age. The nautilus, on the other hand, is represented in the Eocene clay of London by the three large and beautiful species, N. imperialis, N. regalis, and N. urbanus, many of which have been found during the progress of engineering works-such as the tunnels of the Midland and London and North-Western Railways through the clay lying on the southern flank of Hampstead Heath, and in various well-borings. In these specimens, the nacre retains much of its delicate iridescent hue.

Judged by their teeth-three or four inches in length -the sharks are of huge size. Both the bony and cartilaginous fishes abound, and perhaps nearly onehalf of them belong to existing genera-including the very characteristic Pleuronectidæ, or turbots, soles, etc. Among reptiles, there are several species of turtles, tortoises, and lizards; and it is a noteworthy fact that forms, so widely separated geographically as the American alligators and the Indian gavials, should have inhabited the same waters in the south-west of England